Various discrete electrode separators or separation layers for energy storage devices are known. For example, typical separators often consist of a separate porous membrane or sheet which is subsequently (post-fabrication) soaked in an electrolyte and then individually placed and laminated in between two electrodes and the other compositions utilized in the particular device, such as a lithium ion battery. Such a placement and lamination process, however, limits manufacturing throughput and is comparatively expensive. In addition, such lamination processes are not amenable to creating an energy storage device having a substantially flat form factor, and instead typically create a bubble, blister or pillow-shaped device, especially when volatile electrolytes are used and, as a result, are unable to create a series of energy storage cells stably stacked one on top of the other.
Various gelatinous (“gel”) separators are also known but are not amenable for use in a printing process. For example, the known gel separators have insufficient structural strength and cannot withstand the physical forces applied during a printing process such as screen printing, resulting in insufficient electrode separation and electrical shorting of the electrodes.
Other known separation techniques have included the provision of embedded separators within the electrodes themselves. Such electrodes, however, must be formed as separate sheets and a lamination or other assembly process also must be utilized for device fabrication, again being comparatively expensive and limiting throughput, as the forces generated in any type of printing process would also result in insufficient electrode separation and electrical shorting of the electrodes.
As a result, a need remains for a liquid or gel separator utilized to separate and space apart first and second electrodes of an energy storage device, such as a battery or a supercapacitor, and which is formed from a composition that is capable of being printed on a wide variety of surfaces, including irregular, uneven or otherwise non-smooth surfaces, for example and without limitation. A resulting separator also may be flexible and capable of being printed or otherwise applied in a wide variety of configurations, shapes, and form factors. Such a separator should also be comparatively thin to minimize or diminish resistivity or other impedance and have a comparatively high ionic conductivity. In addition, a resulting separator should have sufficient structural strength and integrity to allow and facilitate the printing of additional layers, such as additional electrodes and intervening energy storage materials and compositions.